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Unix EOF

Posted on 2010-08-17
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Last Modified: 2012-05-10
Hi,

I have something in my code as  
PGNWCC01 <<EOF
nwccpr01
EOF
Can u please explain me the above code snippet?
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Question by:r4ranjor
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by:Pieter Jordaan
ID: 33461970

 << means that input follows
EOF tells it to continue reading until it gets another EOF.

You can change it to anything, but it has to be unique. If there is an EOF anywhere else in the text that follow, it will stop reading.

This will also work:
PGNWCC01 <<READLINES
nwccpr01
READLINES
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by:point_pleasant
ID: 33477955
A simple tutorial on UNIX "Here is" Command

A here document is used to redirect input into an interactive shell script or program.

We can run an interactive program within a shell script without user action by supplying the required input for the interactive program, or interactive shell script.

The general form for a here document is:

command << delimiter
document
delimiter
 

Here the shell interprets the << operator as an instruction to read input until it finds a line containing the specified delimiter. All the input lines up to the line containing the delimiter are then fed into the standard input of the command.

The delimiter tells the shell that the here document has completed. Without it, the shell continues to read input forever. The delimiter must be a single word that does not contain spaces or tabs.

Following is the input to the command wc -l to counto total number of line:

[amrood]$wc -l << EOF
      This is a simple lookup program
      for good (and bad) restaurants
      in Cape Town.
EOF
3
[amrood]$
 

You can use here document to print multiple lines using your script as follows:

#!/bin/sh

cat << EOF
This is a simple lookup program
for good (and bad) restaurants
in Cape Town.
EOF      
 

This would produce following result:

This is a simple lookup program
for good (and bad) restaurants
in Cape Town.
 

The following script runs a session with the vi text editor and save the input in the file test.txt.

#!/bin/sh

filename=test.txt
vi $filename <<EndOfCommands
i
This file was created automatically from
a shell script
^[
ZZ
EndOfCommands
 

If you run this script with vim acting as vi, then you will likely see output like the following:

[amrood]$ sh test.sh
Vim: Warning: Input is not from a terminal
[amrood]$
 

After running the script, you should see the following added to the file test.txt:

[amrood]$ cat test.txt
This file was created automatically from
a shell script
[amrood]$
 
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